Multilayer printed board with a double plane spiral interconnection structure

ABSTRACT

An inductor device having plural spiral-shaped interconnection structures connected to each other and extending in plural power source layers, the power source layers being in different levels of a multilayer printed board. The printed board having first and second current loops. The loops share part of a common current path.

BACKGROUND OF THE INVENTION

The present invention relates to a multilayer printed board, and moreparticularly to a multilayer printed board with a double plane spiralinterconnection structure for suppressing electromagnetic interference.

The multilayer printed board has a power source layer and a groundlayer. A high frequency current flows through the power source layer tooperate integrated circuits or large scale integrated circuits. It isnecessary to prevent the high frequency current from so flowing as todraw a large current loop between the power source layer and the groundlayer. In Japanese laid-open patent publication No. 9-139573, it isdisclosed to emphasize the power de-coupling, wherein the power sourcelayer has interconnections which include an impedance-circuit in theform of zigzag, winding crossing or spiral for forming an impedance, andalso insulation layers sandwiching the power source layer are made of aninsulator mixed with a magnetic material.

The conventional multilayer printed board has the following twoproblems.

The first problem is that when the IC or LSI mounted on the multilayerprinted board operates, a high frequency current flows from the IC orLSI to the power source layer, whereby a power system comprising thepower source layer and the ground layer allows a large current loopserving as a looped antenna from which electromagnetic waves as noisesare radiated.

The second problem is that in switching IC or LSI, a current from thepower source layer to the IC or LSI causes a voltage variation the powersource layer. This voltage variation causes a stationary wave in thepower system serving as a looped antenna from which electromagneticwaves as noises are radiated.

In the above circumstances, it had been required to develop a novelmultilayer printed board free from the above problem.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novelmultilayer printed board free from the above problems.

It is a further object of the present invention to provide a novelmultilayer printed board capable of suppressing a radiationelectromagnetic noise from a power source layer of the multilayerprinted board.

The first present invention provides an inductor device comprisingplural spiral-shaped interconnection structures being connected to eachother and extending in plural power source layers differing in level ina multilayer printed board, wherein the plural spiral-shapedinterconnection structures.

The above and other objects, features and advantages of the presentinvention will be apparent from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments according to the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a fragmentary cross sectional elevation view illustrative of amultilayer printed board to which the present invention is applied in afirst preferred embodiment in accordance with the present invention.

FIG. 2A is a plan view illustrative of an inductor device provided in apower source layer in the multilayer printed board of FIG. 1.

FIG. 2B is a perspective view illustrative of an inductor deviceprovided in a power source layer in the multilayer printed board of FIG.1.

FIG. 3 is a fragmentary schematic view illustrative of the inductordevices of FIGS. 2A and 2B and main and branch lines.

FIG. 4 is a fragmentary cross sectional elevation view illustrative of amodified inductor device, wherein an insulative magnetic layer isprovided between paired two spiral-formed interconnection structureswhich form the inductor device.

FIG. 5 is a fragmentary cross sectional elevation view illustrative of amultilayer printed board having the novel inductor devices, wherein LSIcircuits and capacitors are provided on the multilayer printed board.

FIG. 6 is a schematic view illustrative of a measuring system formeasuring a characteristic impedance of the inductor device shown inFIG. 2.

FIG. 7 is a diagram illustrative of variation in characteristicimpedance of the inductor device in a time domain reflectometry by useof the measuring system of FIG. 6.

FIG. 8 is a schematic view illustrative of a measuring system formeasuring an S-parameter of the inductor device shown in FIG. 2.

FIG. 9 is a diagram illustrative of variation in |S21| of the inductordevice over frequency by use of the measuring system of FIG. 8.

FIG. 10 is a fragmentary cross sectional elevation view illustrative ofa further modified inductor device, wherein a single inner insulativemagnetic layer is provided between paired two spiral-formedinterconnection structures which form the inductor device and furtherpaired two outer insulative magnetic layers are provided so that theupper and lower power source layers are positioned between the pairedtwo insulative magnetic layers.

FIG. 11 is a fragmentary cross sectional elevation view illustrative ofanother multilayer printed board to which the present invention isapplied in a third preferred embodiment in accordance with the presentinvention.

DISCLOSURE OF THE INVENTION

The first present invention provides an inductor device comprisingplural spiral-shaped interconnection structures being connected to eachother and extending in plural power source layers differing in level ina multilayer printed board.

It is preferable that the plural spiral-shaped interconnectionstructures comprises first and second spiral-shaped interconnectionstructures extending in first and second power source layers in firstand second levels, respectively.

It is also preferable that the multilayer printed board has at least afirst high frequency current loop with a first loop area and a secondhigh frequency current loop with a second loop area which is larger thanthe first loop area, and the first high frequency current loop and thesecond high frequency current loop have a partially common current path,and the first frequency current loop has a first current path includingany one of the paired power source layers and excluding the inductordevice and remaining one of the paired power source layers.

It is also preferable that the plural spiral-shaped interconnectionstructures extends in plane and are connected to each other at thesecenter portions.

It is also preferable that the plural spiral-shaped interconnectionstructures have the same current directions as each other.

It is also preferable that each of the plural spiral-shapedinterconnection structures has a spiral pitch of not more than 1 mm.

It is also preferable to further comprise an inside insulative magneticlayer between adjacent two of the plural spiral-shaped interconnectionstructures. In this case, it is further preferable that the insideinsulative magnetic layer comprises a mixture of a resin material andmagnetic powders. It is furthermore preferable to further compriseoutside insulative magnetic layers in opposite sides of the plural powersource layers so that the plural power source layers are positionedbetween the outside insulative magnetic layers. In this case, it is alsopreferable that the outside insulative magnetic layers comprise amixture of a resin material and magnetic powders.

It is also preferable that, in the multilayer printed board, dielectriclayers sandwiching the power source layers are higher in dielectric lossthan other dielectric layers.

The second present invention provides a multilayer printed board havingplural signal layers, plural power source layers, plural ground layers,and the multilayer printed board also having at least a first highfrequency current loop with a first loop area and a second highfrequency current loop with a second loop area which is larger than thefirst loop area, and the first high frequency current loop and thesecond high frequency current loop have a partially common current path,wherein the multilayer printed board further has at least an inductordevice in the plural power source layers, so that the first frequencycurrent loop has a first current path including any one of the pairedpower source layers and excluding the inductor device and remaining oneof the paired power source layers.

It is preferable that the at least inductor device comprises pluralspiral-shaped interconnection structures being connected to each otherand extending in plural power source layers differing in level in amultilayer printed board, wherein the plural spiral-shapedinterconnection structures.

It is also preferable that the plural spiral-shaped interconnectionstructures comprises first and second spiral-shaped interconnectionstructures extending in first and second power source layers in firstand second levels, respectively.

It is also preferable that the plural spiral-shaped interconnectionstructures extend in plane and are connected to each other at thesecenter portions.

It is also preferable that the plural spiral-shaped interconnectionstructures have the same current directions as each other.

It is also preferable that each of the plural spiral-shapedinterconnection structures has a spiral pitch of not more than 1 mm.

It is also preferable to further comprise an inside insulative magneticlayer between adjacent two of the plural spiral-shaped interconnectionstructures. In this case, it is also preferable that the insideinsulative magnetic layer comprises a mixture of a resin material andmagnetic powders. It is further more preferable to further compriseoutside insulative magnetic layers in opposite sides of the plural powersource layers so that the plural power source layers are positionedbetween the outside insulative magnetic layers. In this case, it is alsopreferable that the outside insulative magnetic layers comprise amixture of a resin material and magnetic powders.

It is also preferable that, in the multilayer printed board, dielectriclayers sandwiching the power source layers are higher in dielectric lossthan other dielectric layers.

The present invention provides a multilayer printed board having a powersource layer in the vicinity of a device such as an integrated circuitor a large scale integrated circuit, wherein the power source layer hasa double plane spiral interconnection structure which comprises a firstlevel interconnection extending in the shape of spiral included in afirst level plane and a second level interconnection extending in theshape of spiral included in a second level plane, and the first leveland second level interconnections are connected to each other at thosecenter positions so that a current direction is the same between thefirst level and second level interconnections.

The above double plane spiral interconnection structure in the vicinityof the device such as the IC or LSI serves as an inductor device whichemphasizes the power de-coupling of the IC or LSI. This emphasis of thepower de-coupling of the IC or LSI reduces an effective area of a loopof a high frequency current generated in a power system comprising thepower source layer and a ground layer. The above double plane spiralinterconnection structure in the power source layer increases a loss dueto electromagnetic wave propagation through the power system comprisingthe power source layer and the ground layer. Namely, the above doubleplane spiral interconnection structure in the power source layerincreases a conductor loss due to a conductor existing in the powersource layer and a dielectric loss due to a dielectric existing in thepower system comprising the power source layer and the ground layer. Theincrease of the loss due to electromagnetic wave propagation or theconductor loss and the dielectric loss causes an attenuation of thestationary wave generated in the power system.

It is also available that an insulation magnetic material layer isprovided between the first level and second level interconnections sothat the insulation magnetic material layer extends in an entire regionof the multilayer printed board.

The provision of the insulation magnetic material layer between thefirst level and second level interconnections increase an inductance ofthe inductor device comprising the double plane spiral interconnectionstructure because the magnetic material contained in the insulationmagnetic material layer has a complex relative permeability with a realpart of not less than 1. The increase in inductance of the inductorfurther emphasizes the de-coupling of the IC or LSI. This furtheremphasis of the de-coupling of the IC or LSI further reduces theeffective area of the loop of the high frequency current generated inthe power system comprising the power source layer and a ground layer.In a frequency range, where an imaginary part of the above complexrelative permeability of the magnetic material contained in theinsulation magnetic material layer is more than 0, the magnetic materialcauses the loss due to the electromagnetic wave propagation. Theincrease of the loss due to electromagnetic wave propagation causes afurther attenuation of the stationary wave generated in the powersystem.

Preferred Embodiment

First Embodiment:

A first embodiment according to the present invention will be describedin detail with reference to the drawings. FIG. 1 is a fragmentary crosssectional elevation view illustrative of a multilayer printed board towhich the present invention is applied in a first preferred embodimentin accordance with the present invention. The multilayer printed boardcomprises alternating laminations of a plurality of dielectric layers 5and any one of signal layers 2, ground layers 3 and power source layers4. One of the dielectric layers 5 is sandwiched between the two powersource layers 4. The two power source layers 4 are further sandwichedbetween the other two dielectric layers 5 to form a five layerlamination structure. This five layer lamination structure is furthersandwiched between the two ground layers 3 to form a seven layerlamination structure. This seven layer lamination structure is furthersandwiched between the still other two dielectric layers 5 to form anine layer lamination structure. This nine layer lamination structure isfurthermore sandwiched between the signal layers 2.

FIG. 2A is a plan view illustrative of an inductor device provided in apower source layer in the multilayer printed board of FIG. 1. FIG. 2B isa perspective view illustrative of an inductor device provided in apower source layer in the multilayer printed board of FIG. 1. Each ofthe power source layers 4 in the vicinity of an IC or an LSI has aninductor device 10. The indicator device 10 comprises a pair of at leasttwo spiral-formed interconnection structures, each of which comprises aninterconnection extending in the plane of the power source layers 4 inthe form of a spiral. The paired two spiral-formed interconnectionstructures are formed in adjacent two different level power sourcelayers 4 which are isolated by the single dielectric layer 5, whereinthe paired two spiral-formed interconnection structures extend to formparallel planes to each other, so that the paired two spiral-formedinterconnection structures are positioned to overlap to each other andtwo planes formed by the paired two spiral-formed interconnectionstructures face to each other. The paired two spiral-formedinterconnection structures are connected to each other to form a spiralcurrent loop pair. Usually, it is preferable that center portions of thepaired two spiral-formed interconnection structures are connectedthrough a connection line extending in a vertical direction to theplanes of the paired two spiral-formed interconnection structures asshown in FIG. 2B. The connection line extends through the dielectriclayer 5 in the vertical direction to the planes of the paired twospiral-formed interconnection structures. Notwithstanding, it ispossible as a modification to the above structure that the paired twospiral-formed interconnection structures are connected at otherpositions than the center portions. In this modified case, the pairedtwo spiral-formed interconnection structures are connected through theconnection line which extends through the dielectric layer 5 in thevertical direction to the planes of the paired two spiral-formedinterconnection structures. It is preferable that currents flow throughthe spiral-formed interconnections in the same spiral directions betweenthe paired two spiral-formed interconnection structures. It is, however,possible as a modification to the above structure that currents flowthrough the spiral-formed interconnections in opposite spiral directionsbetween the paired two spiral-formed interconnection structures, even inthis case, an obtained inductance is smaller than the above case wherethe currents flow in the same spiral directions. In FIGS. 2A, and 2B,the lower one 6 b of the paired two spiral-formed interconnectionstructures is represented by “6 b”, whilst the upper one thereof isrepresented by “6 a”. It is possible that the spiral shape is square asshown in FIGS. 2A and 2B. It is, however, possible to modify the squareshape of the spiral into other shapes, for example, rectangles, circles,and ovals. It is also preferable that a pitch of the spiral is not morethan 1 mm in order to keep a high inductance of the inductor device 10.

As described above, the inductor device 10 comprises the paired twospiral-formed interconnection structures. This inductor device 10 isprovided in the power source layer 4 but in the vicinity of the IC orLSI. This inductor device 10 provides a high impedance to the highfrequency current flowing through the power system in the multilayerprinted board. This high impedance to the high frequency current causesthat a majority of the high frequency current flowing from the IC or LSIthrough the power source layer is by-passed to a capacitor which ispositioned nearest thereto, thereby to reduce a high frequency currentloop formed in the power system of the multilayer printed board.

The inductor device 10 also serves to attenuate the stationary wave tobe generated in the power source layer in the multilayer printed board.The above paired two spiral-formed interconnection structures increasethe loss in the electromagnetic wave propagation through the powersystem in the multilayer printed board.

Accordingly, the inductor device 10 suppresses the electromagneticnoises radiated from the power system in the multilayer printed circuitboard.

FIG. 3 is a fragmentary schematic view illustrative of the inductordevices of FIGS. 2A and 2B and main and branch lines. The inductordevice 10 is connected to a main line 8 which extends at the same levelas one of the paired two spiral-formed interconnection structures.Adjacent two of the inductor devices 10 are connected through a branchline 9 which extends at the same level as another of the paired twospiral-formed interconnection structures.

FIG. 4 is a fragmentary cross sectional elevation view illustrative of amodified inductor device, wherein an insulative magnetic layer isprovided between paired two spiral-formed interconnection structureswhich form the inductor device. A single insulative magnetic layer 14 isprovided at an intermediate level 7 between the upper and lower powersource layers 4, so that the single insulative magnetic layer 14 extendsbetween the paired two spiral-formed interconnection structures 6 a and6 b formed in the upper and lower power source layers 4. The singleinsulative magnetic layer 14 extends on entire regions of the substrate.The single insulative magnetic layer 14 may, for example, be made of aresin distributed with magnetic powders. Namely, the inductor device 10comprises the paired two spiral-formed interconnection structures 6 aand 6 b and the single insulative magnetic layer 14. The provision ofthe insulative magnetic layer 14 between the first level and secondlevel interconnections increase an inductance of the inductor devicecomprising the double plane spiral interconnection structure because themagnetic material contained in the insulative magnetic layer 14 has acomplex relative permeability with a real part of not less than 1. Theincrease in inductance of the inductor further emphasizes thede-coupling of the IC or LSI. This further emphasis of the de-couplingof the IC or LSI further reduces the effective area of the loop of thehigh frequency current generated in the power system comprising thepower source layer and a ground layer. In a frequency range, where animaginary part of the above complex relative permeability of themagnetic material contained in the insulative magnetic layer 14 is morethan 0, the magnetic material causes the loss due to the electromagneticwave propagation. The increase of the loss due to electromagnetic wavepropagation causes a further attenuation of the stationary wavegenerated in the power system.

FIG. 5 is a fragmentary cross sectional elevation view illustrative of amultilayer printed board having the novel inductor devices, wherein LSIcircuits and capacitors are provided on the multilayer printed board.The multilayer printed board has upper and lower power source layers 4which are isolated by a dielectric layer 5. Upper and lower groundlayers 3 are also provided over and under the upper and lower powersource layers 4 through the dielectric layers 5. Upper and lower signallayers 2 are also provided over and under the upper and lower powersource layers 4 through the dielectric layers 5 respectively. On theupper signal layer 2, LSI circuits 12 a and 12 b and capacitors 13 a and13 b are provided. The LSI circuit 12 a is connected through contactlines 11 to the upper ground layer 3 and the upper power source layer 4.The capacitor 13 a is also connected through contact lines 11 to theupper ground layer 3 and the upper power source layer 4. The LSI circuit12 b is connected through contact lines 11 to the upper ground layer 3and the lower power source layer 4. The capacitor 13 b is also connectedthrough contact lines 11 to the upper ground layer 3 and the lower powersource layer 4. Each of the inductor devices 10 comprises a pair ofupper and lower spiral-formed interconnection structures 6 a and 6 b inthe upper and lower power source layers 4 respectively. The upperspiral-formed interconnection structure 6 a comprises an interconnectionextending in the form of a spiral in plane of the upper power sourcelayers 4. The lower spiral-formed interconnection structure 6 bcomprises an interconnection extending in the form of a spiral in planeof the lower power source layers 4. The upper and lower spiral-formedinterconnection structures 6 a and 6 b extend to form parallel planes toeach other, so that the upper and lower spiral-formed interconnectionstructures 6 a and 6 b are positioned to overlap to each other and twoplanes formed by the upper and lower spiral-formed interconnectionstructures 6 a and 6 b face to each other. The upper and lowerspiral-formed interconnection structures 6 a and 6 b are connected toeach other to form a spiral current loop pair, wherein center portionsof the upper and lower spiral-formed interconnection structures 6 a and6 b are connected through a connection line 7 extending in a verticaldirection to the planes of the upper and lower spiral-formedinterconnection structures 6 a and 6 b. The connection line 7 extendsthrough the dielectric layer 5 in the vertical direction to the planesof the upper and lower spiral-formed interconnection structures 6 a and6 b. Currents flow through the spiral-formed interconnections in thesame spiral directions between the paired two spiral-formedinterconnection structures. The spiral shape is square and a pitch ofthe spiral is not more than 1 mm in order to keep a high inductance ofthe inductor device 10.

During operation of the LSI circuit 12 a, a high frequency current flowsfrom the LSI circuit 12 a through the connection line 11 and the upperpower source layer 4. A part of this high frequency current flowsthrough the connection line 11, the capacitor 13 a, the connection line11 and the upper ground layer 3 and returned through the connection lineto the LSI circuit 12 a. Another part of the high frequency currentflows through the inductor device 10 to the lower power source line 4,the connection line 11, the capacitor 13 b, the connection line 11 andthe upper ground layer 3 and returned through the connection line to theLSI circuit 12 a. Namely, two different current loops are formed. Thefirst current loop is formed by the upper power source layer 4, thecapacitor 13 a and the upper ground line 3. The second current loop isformed by the upper power source layer 4, the inductor device 10, thelower power source layer 4, the capacitor 13 b and the upper ground line3. As can be seen from FIG. 5, the first current loop is smaller thanthe second current loop. The small current loop causes a smallelectromagnetic noise radiation. The large current loop causes a largeelectromagnetic noise radiation. The power current is applied from thepower source layer 4 for switching operation of the LSI circuits 12 aand 12 b. This power current causes variation in voltage level of thepower system comprising the power source layer 4 and the ground layer 3.This variation in voltage level of the power system generates astationary wave in the power system. In accordance with the presentinvention, however, the inductor device 10 is provided in the upper andlower power source layers 4. Namely, the inductor device 10 is providedin the larger current loop. The smaller current loop is, however, freeof the inductor device 10. This inductor device 10 serves as a highimpedance device to the high frequency current flowing through the powersource layers 4. This inductor device 10 relatively decreases the secondcurrent part flowing through the second loop or the larger loop andrelatively increase the first current part flowing through the firstloop or the smaller loop. Namely, the inductor device 10 causes amajority of the high frequency current to flow through the first currentloop which is smaller than the second current loop. As described above,the small current loop causes a small electromagnetic noise radiation,whilst the large current loop causes a large electromagnetic noiseradiation. The reduction in the second current flowing through thesecond loop larger than the first current loop results in a certainreduction in the electromagnetic noise radiation from the power system.

A ratio of the larger current loop or the second current loop to thesmaller current loop or the first current loop varies over the currentfrequency. Variation in ratio of the larger current loop or the secondcurrent loop to the smaller current loop or the first current loopvaries over the current frequency depends upon the frequencycharacteristic of the inductance of the inductor device 10. At acritical frequency where the inductance value is beginning to decrease,the ratio of the larger current loop or the second current loop to thesmaller current loop or the first current loop is beginning to increase.

Further, if the power source layers 4 are structured as shown in FIG. 3,then the generation of the electromagnetic wave in the power system inswitching operation to the LSI circuits 12 a and 12 b increases the lossdue to the electromagnetic wave propagation through the power system.The increase in the loss due to the electromagnetic wave propagationthrough the power system attenuates the stationary wave generated in thepower system, whereby the radiation electromagnetic noise is suppressed.

Furthermore, if the insulative magnetic layer 14 is provided between theupper and lower spiral-formed interconnection structures 6 a and 6 b ofthe inductor device 10 as shown in FIG. 4, a further effect ofsuppression to the radiation electromagnetic noise can be obtained. Theinsulative magnetic layer 14 is provided between the upper and lowerpower source layers 4, so that the single insulative magnetic layer 14extends between the paired two spiral-formed interconnection structures6 a and 6 b formed in the upper and lower power source layers 4. Thesingle insulative magnetic layer 14 extends on entire regions of thesubstrate. The single insulative magnetic layer 14 may, for example, bemade of a resin distributed with magnetic powders. Namely, the inductordevice 10 comprises the paired two spiral-formed interconnectionstructures 6 a and 6 b and the single insulative magnetic layer 14. Theprovision of the insulative magnetic layer 14 between the first leveland second level interconnections increase an inductance of the inductordevice 10 comprising the double plane spiral interconnection structurebecause the magnetic material contained in the insulative magnetic layer14 has a complex relative permeability with a real part of not lessthan 1. The increase in inductance of the inductor further emphasizesthe de-coupling of the IC or LSI. This further emphasis of thede-coupling of the IC or LSI further reduces the effective area of theloop of the high frequency current generated in the power systemcomprising the power source layer and a ground layers In a frequencyrange, where an imaginary part of the above complex relativepermeability of the magnetic material contained in the insulativemagnetic layer 14 is more than 0, the magnetic material causes the lossdue to the electromagnetic wave propagation. The increase of the lossdue to electromagnetic wave propagation causes a further attenuation ofthe stationary wave generated in the power system.

As examples, the number of the spiral of each of the upper and lowerspiral-formed interconnection structures 6 a and 6 b of the inductordevice 10 may be 5. The pitch 16 of the spiral may be set at 0.4 mm. Thespiral shape may be square.

The insulative magnetic layer 14 may, for example, be made of a complexmaterial of 50% by volume of an epoxy resin and 50% by volume of Ni—Znferrite powders.

FIG. 6 is a schematic view illustrative of a measuring system formeasuring a characteristic impedance of the inductor device shown inFIG. 2. FIG. 7 is a diagram illustrative of variation in characteristicimpedance of the inductor device in a time domain reflectometry by useof the measuring system of FIG. 6. The number of the spiral of each ofthe upper and lower spiral-formed interconnection structures 6 a and 6 bof the inductor device 10 is 5. The pitch 16 of the spiral is 0.4 mm.The spiral shape may be square. Measured for the characteristicimpedance are both the first type inductor device 10 including theinsulative magnetic layer 14 made of a complex material of an epoxyresin and Ni—Zn ferrite powders with a thickness of 0.2 mm and thesecond type inductor device 10 free of the insulative magnetic layer 14.In FIG. 7, a region in the vicinity of 50 ohms in characteristicimpedance represents a co-axial cable or a 50 ohms terminator, whilstother regions represent characteristics of the inductor device 10 overindividual positions. “−” represents the characteristic impedance of thefirst type inductor device 10 including the insulative magnetic layer 14made of a complex material of an epoxy resin and Ni—Zn ferrite powderswith a thickness of 0.2 mm, “−” represents the characteristic impedanceof the second type inductor device 10 free of the insulative magneticlayer 14.

At the center position of the inductor device 10, a sharp peak appearswhich represents a rapid increase in the characteristic impedance of theinductor device 10. This inductor device 10 serves as a high impedancedevice to the high frequency current in operation of the IC or LSIcircuits 12 a and 12 b. Namely, the inductor device 10 is provided inthe larger current loop. The smaller current loop is, however, free ofthe inductor device 10. This inductor device 10 serves as a highimpedance device to the high frequency current flowing through the powersource layers 4. This inductor device 10 relatively decreases the secondcurrent part flowing through the second loop or the larger loop andrelatively increase the first current part flowing through the firstloop or the smaller loop. Namely, the inductor device 10 causes that themajority of the high frequency current flows through the first currentloop which is smaller than the second current loop. As described above,the small current loop causes a small electromagnetic noise radiation,whilst the large current loop causes a large electromagnetic noiseradiation. The reduction in the second current flowing through thesecond loop larger than the first current loop results in a certainreduction in the electromagnetic noise radiation from the power system.

FIG. 8 is a schematic view illustrative of a measuring system formeasuring an S-parameter of the inductor device shown in FIG. 2. FIG. 9is a diagram illustrative of variation in |S21| of the inductor deviceover frequency by use of the measuring system of FIG. 8. The number ofthe spiral of each of the upper and lower spiral-formed interconnectionstructures 6 a and 6 b of the inductor device 10 is 5. The pitch 16 ofthe spiral is 0.4 mm. The spiral shape may be square. Measured for thecharacteristic impedance are both the first type inductor device 10including the insulative magnetic layer 14 made of a complex material ofan epoxy resin and Ni—Zn ferrite powders with a thickness of 0.2 mm andthe second type inductor device 10 free of the insulative magnetic layer14. In FIG. 9, “−” represents the variation in |S21| over frequency ofthe first type inductor device 10 including the insulative magneticlayer 14 made of a complex material of an epoxy resin and Ni—Zn ferritepowders with a thickness of 0.2 mm. “−” represents the variation in|S21| over frequency of the second type inductor device 10 free of theinsulative magnetic layer 14. The maximum value of |S21| to the inductordevice 10 decreases as the frequency is increased. This decrease iscaused by the loss due to the electromagnetic wave propagation. In ahigh frequency band of not less than about 160 MHz, the first typeinductor device 10 having the insulative magnetic layer 14 is smaller in|S21| than the second type inductor device 10 free of the insulativemagnetic layer 14 due to the increased loss by the electromagnetic wavepropagation due to existence of the imaginary part of the complexrelative permeability of the complex material for the insulativemagnetic layer 14.

As described above, the inductor device 10 comprises the paired twospiral-formed interconnection structures. This inductor device 10 isprovided in the power source layer 4 but in the vicinity of the IC orLSI. This inductor device 10 provides a high impedance to the highfrequency current flowing through the power system in the multilayerprinted board. This high impedance to the high frequency current causesthat a majority of the high frequency current flowing from the IC or LSIthrough the power source layer is by-passed to a capacitor which ispositioned nearest thereto, thereby to reduce a high frequency currentloop formed in the power system of the multilayer printed board.

The inductor device 10 also serves to attenuate the stationary wave tobe generated in the power source layer in the multilayer printed board.The above paired two spiral-formed interconnection structures increasethe loss in the electromagnetic wave propagation through the powersystem in the multilayer printed board.

Accordingly, the inductor device 10 suppresses the electromagneticnoises radiated from the power system in the multilayer printed circuitboard.

Second Embodiment:

A second embodiment according to the present invention will be describedin detail with reference to the drawings. FIG. 10 is a fragmentary crosssectional elevation view illustrative of a further modified inductordevice, wherein a single inner insulative magnetic layer is providedbetween paired two spiral-formed interconnection structures which formthe inductor device and further paired two outer insulative magneticlayers are provided so that the upper and lower power source layers arepositioned between the paired two insulative magnetic layers. A singleinner insulative magnetic layer 14 is provided at an intermediate level7 between the upper and lower power source layers 4, so that the singleinner insulative magnetic layer 14 extends between the paired twospiral-formed interconnection structures 6 a and 6 b formed in the upperand lower power source layers 4. The single inner insulative magneticlayer 14 extends on entire regions of the substrate. Further, paired twoouter insulative magnetic layers 14 are provided to sandwich the upperand lower power source layers 4 so that the upper and lower power sourcelayers 4 are positioned between the paired two outer insulative magneticlayers 14. The singe inner insulative magnetic layer 14 and the pairedtwo outer insulative magnetic layers 14 may, for examples be made of aresin distributed with magnetic powders. Namely, the inductor device 10comprises the paired two spiral-formed interconnection structures 6 aand 6 b and the single insulative magnetic layer 14. The provision ofthe single inner insulative magnetic layer 14 between the first leveland second level interconnections and the further provision of thepaired two outer insulative magnetic layers 14 to sandwich the upper andlower power source layers 4 increase an inductance of the inductordevice comprising the double plane spiral interconnection structurebecause the magnetic material contained in the insulative magneticlayers 14 has a complex relative permeability with a real part of notless than 1. The increase in inductance of the inductor furtheremphasizes the de-coupling of the IC or LSI. This further emphasis ofthe de-coupling of the IC or LSI further reduces the effective area ofthe loop of the high frequency current generated in the power systemcomprising the power source layer and a ground layer. In a frequencyrange, where an imaginary part of the above complex relativepermeability of the magnetic material contained in the insulativemagnetic layers 14 is more than 0, the magnetic material causes the lossdue to the electromagnetic wave propagation. The increase of the lossdue to electromagnetic wave propagation causes a further attenuation ofthe stationary wave generated in the power system.

Third Embodiment:

A third embodiment according to the present invention will be describedin detail with reference to the drawings. FIG. 11 is a fragmentary crosssectional elevation view illustrative of another multilayer printedboard to which the present invention is applied in a third preferredembodiment in accordance with the present invention. The multilayerprinted board comprises alternating laminations of a plurality of firstand second type dielectric layers 5 and 15 and signals layers 2, groundlayers 3 and power source layers 4. The second type dielectric layers 15have a larger dielectric loss than the first type dielectric layers 15.One of the second type dielectric layers 15 is sandwiched between thetwo power source layers 4. The two power source layers 4 are furthersandwiched between the remaining two second type dielectric layers 15 toform a five layer lamination structure. This five layer laminationstructure is further sandwiched between the two ground layers 3 to forma seven layer lamination structure. This seven layer laminationstructure is further sandwiched between the two first type dielectriclayers 5 to form a nine layer lamination structure. This nine layerlamination structure is furthermore sandwiched between the signal layers2. In this embodiment, the second type dielectric layers 15 which have alarger dielectric loss than the first type dielectric layers 5, so as toattenuate the stationary wave generated in the power system comprisingthe power source layer and the ground layer, whereby the radiationelectromagnetic noise from the power system is further reduced.

Whereas modifications of the present invention will be apparent to aperson having ordinary skill in the art, to which the inventionpertains, it is to be understood that embodiments as shown and describedby way of illustrations are by no means intended to be considered in alimiting sense. Accordingly, it is to be intended to cover by claims allmodifications which fall within spirit and scope of the presentinvention.

1. A multilayer printed board having plural signal layers, plural powersource layers, plural ground layers, and said multilayer printed boardalso having at least a first high frequency current loop with a firstloop area and a second high frequency current loop with a second looparea which is larger than said first loop area, and said first highfrequency current loop and the second high frequency current loop have apartially common current path, wherein said multilayer printed boardfurther has at least an inductor device in said plural power sourcelayers, so that said first frequency current loop has a first currentpath including any one of said paired power source layers and excludingsaid inductor device and remaining one of said paired power sourcelayers, and wherein said at least inductor device comprises pluralspiral-shaped interconnection structures being connected to each otherand extending in plural power source layers differing in level in amultilayer printed board.
 2. The multilayer printed board as claimed inclaim 1, wherein said plural spiral-shaped interconnection structurescomprises first and second spiral-shaped interconnection structuresextending in first and second power source layers in first and secondlevels, respectively.
 3. The multilayer printed board as claimed inclaim 1, wherein said plural spiral-shaped interconnection structuresextend in plane and are connected to each other at these centerportions.
 4. The multilayer printed board as claimed in claim 1, whereinsaid plural spiral-shaped interconnection structures have the samecurrent directions as each other.
 5. The multilayer printed board asclaimed in claim 1, wherein each of said plural spiral-shapedinterconnection structures has a spiral pitch of not more than 1 mm. 6.The multilayer printed board as claimed in claim 1, further comprisingan inside insulative magnetic layer between adjacent two of said pluralspiral-shaped interconnection structures.
 7. The multilayer printedboard as claimed in claim 6, wherein said inside insulative magneticlayer comprises a mixture of a resin material and magnetic powders. 8.The multilayer printed board as claimed in claim 6, further comprisingoutside insulative magnetic layers in opposite sides of said pluralpower source layers so that said plural power source layers arepositioned between said outside insulative magnetic layers.
 9. Themultilayer printed board as claimed in claim 8, wherein said outsideinsulative magnetic layers comprise a mixture of a resin material andmagnetic powders.
 10. A multilayer printed board having plural signallayers, plural power source layers, plural ground layers, and saidmultilayer printed board also having at least a first high frequencycurrent loop with a first loop area and a second high frequency currentloop with a second loop area which is larger than said first loop area,and said first high frequency current loop and the second high frequencycurrent loop having a partially common current path, wherein saidmultilayer printed board further has at least an inductor device in saidplural power source layers, so that said first frequency current loophas a first current path including any one of said paired power sourcelayers and excluding said inductor device and remaining one of saidpaired power source layers, and wherein in said multilayer printedboard, dielectric layers sandwiching said power source layers are higherin dielectric loss than other dielectric layers.